This proposal involves an investigation of the molecular mechanism of enterotoxin B (SEB) production and its control in Staphylococcus aureus: It also involves studies on the role of plasmids in enterotoxinogenesis. The experimental approach would involve the following: localization and isolation of SEB determinants by insertional inactivation with transposons and transduction from both plasmid positive and negative strains; cloning of the determinants on a vector plasmid; and studies on the ability of such chimeric plasmids to produce SEB. A small plasmid (pSN2) has been implicated in the synthesis of SEB, but it does not code for the structure of this toxin. The precise role of this plasmid in enterotoxin B production and the mechanism by which pSN2 coded polypeptides effect SEB production would be investigated. Experiments would be performed to evaluate the possible role of this plasmid in the following processes: transcription of the toxin message; translation of the toxin message; processing of toxin polypeptide; secretion of toxin; and some other unsuspected control process.